FTA: "This isn't about me. This is about passion and about pursuing your dreams," he said. "Everyone has their own personal telescopeEl Guapo - maybe it's making an amazing wedding dress for your daughter. So you learn to sew and you make that dress. You don't have to be a fancy person. Anyone can achieve their dreams."

Yeah, I should be able to use this. This guy's worked with members of the Salt Lake Astronomical Society, and the people he's been working with have been discussing the 'scope, as well as his desire to let people use it, for the year that I've been a member. I missed a chance last December to see it while it was under construction. There are a lot of home-built telescopes here, even a couple of guys with observatories in their houses, but this is obviously the biggest. Some of these guys even make their own mirrors. Me, I can make beer and beef jerky, and that's about it.

It's kind of cool that I can get to use this thing(If I re-up my membership, that is... ).

Marcus Aurelius:I just wonder what a dinged KH-12 mirror would sell for, and who would want it.

As I recall, this guy got his mirror for a pretty good deal, all things considered. I mean, it seems like he almost got it for free since it was just a throwaway anyway. I think the main rig has cost him a lot though.

Like I said, time to quit dragging ass and get back into touch with these people so that I can look through this baby.

dittybopper:Cold_Sassy: That is one of the coolest things I've read on this site, ever.

Oh, sure, but it's a Dobsonian, so it's crap because he doesn't have it on an equatorial mount.

LOL, and yet... something with that focal length is going to have a HUGE magnification, unless you somehow cobble together something that acts like a ten-inch focal length eyepiece (in which case you'll be throwing away most of the light, since the exit pupil would be enormous). With a nice "wide-angle" eyepiece you'd be looking at something like 400x, and you'd be able to keep an object in your field of view for maybe a couple of seconds without tracking.

But I'll bet he's got something cobbled together to make that work. I'm still not sure what the image quality will be like -- supporting a 70-inch mirror designed for a free-fall environment should be loads (ahem) of fun -- but kudos to him for getting it this far. I'd love to see more details.

jfarkinB:dittybopper: Cold_Sassy: That is one of the coolest things I've read on this site, ever.

Oh, sure, but it's a Dobsonian, so it's crap because he doesn't have it on an equatorial mount.

LOL, and yet... something with that focal length is going to have a HUGE magnification, unless you somehow cobble together something that acts like a ten-inch focal length eyepiece (in which case you'll be throwing away most of the light, since the exit pupil would be enormous). With a nice "wide-angle" eyepiece you'd be looking at something like 400x, and you'd be able to keep an object in your field of view for maybe a couple of seconds without tracking.

But I'll bet he's got something cobbled together to make that work. I'm still not sure what the image quality will be like -- supporting a 70-inch mirror designed for a free-fall environment should be loads (ahem) of fun -- but kudos to him for getting it this far. I'd love to see more details.

Supposing your assembled scope weighs in at around an even metric ton, with a diameter of about 3 meters, how big an equatorial mount would we be talking about here? It would have to be massive.

Marcus Aurelius:jfarkinB: Supposing your assembled scope weighs in at around an even metric ton, with a diameter of about 3 meters, how big an equatorial mount would we be talking about here? It would have to be massive.

More than massive enough to make it a stupid idea. You'd want some sort of computer-driven altazimuth mount. Even an altaz drive this size would be big fun, but at least you wouldn't have to worry about suspending a ton several feet out from a precision-bearing fulcrum.

You'd still have to deal with field rotation, but that's completely independent of scope size. For a 12-megapixel sensor, I think you'd trail around 10 pixels per minute at the edges of the image. Crop or bin your image and stack short exposures, or build a camera rotator (should be relatively easy because of the lighter load), or insert a rotating prism/mirror element that's driven. I haven't looked into this, but I'm sure it must be a solved problem.

That's pretty cool. How good does it work? I did some optical design and played around a lot with Zemax back in my undergraduate days, and while getting functional optics together wasn't hard, getting high quality optics without resorting to magical materials is actually really tricky.

error 303:That's pretty cool. How good does it work? I did some optical design and played around a lot with Zemax back in my undergraduate days, and while getting functional optics together wasn't hard, getting high quality optics without resorting to magical materials is actually really tricky.

Wow, that's great. Looks like some kind of off axis design so that he can have the eyepiece lower on the middle of the scope instead of way up at the top which would be super hard to get to. That's why the secondary is so big, did I read 20 inches? It still only blocks 20*20/70/70*100 or about 8 percent of the light.

Bet he got the mirror from here, http://gsaauctions.gov/gsaauctions/gsaauctions/ although this week there are 0 items on the NASA Shuttle/Hubble sales portion. I have seen some neat stuff on this site go for good prices and some stuff that the bidders got the fever and drove the price past reasonable to more than retail.

Ok, serious tech question. He's assuming this came off a spy satellite- it's a bit unclear what kind since Wikipedia implies the KH-11s are f1.2 and thus aren't this mirror. Most serious telescopes are not standard Newtonians- the Hubble a Ritchey Chretien, Wiki says the KH-11s are three mirror anastigmats. In either case, the secondary is not a flat mirror- it's curved in some odd way. (RCs are hyperbolic, for example)

Where the fark did he get a curved, 29" secondary? No way did he grind it himself- did it come with the primary?

Glockenspiel Hero:Ok, serious tech question. He's assuming this came off a spy satellite- it's a bit unclear what kind since Wikipedia implies the KH-11s are f1.2 and thus aren't this mirror. Most serious telescopes are not standard Newtonians- the Hubble a Ritchey Chretien, Wiki says the KH-11s are three mirror anastigmats. In either case, the secondary is not a flat mirror- it's curved in some odd way. (RCs are hyperbolic, for example)

Where the fark did he get a curved, 29" secondary? No way did he grind it himself- did it come with the primary?

He could have paid someone to grind it for him, in theory for as little as 10 grand. Which may sound like a lot but isnt, for a project this size.

Im sure the beast has lots of distortion but generates cool views anyway. Even a 14" telescope is massive, a 70" is a monster.

Well, that's even more baffling. What's the stripy pointy thing for? Where does the eyepiece or sensor go? Is it actually off-axis (angled secondary), or is there a tertiary flat somewhere, or is there a hole too small to see in the center of the primary?

Glockenspiel Hero:Ok, serious tech question. He's assuming this came off a spy satellite- it's a bit unclear what kind since Wikipedia implies the KH-11s are f1.2 and thus aren't this mirror. Most serious telescopes are not standard Newtonians- the Hubble a Ritchey Chretien, Wiki says the KH-11s are three mirror anastigmats. In either case, the secondary is not a flat mirror- it's curved in some odd way. (RCs are hyperbolic, for example)

Where the fark did he get a curved, 29" secondary? No way did he grind it himself- did it come with the primary?

The secondary mirror on a Dobsonian telescope are flat (at least in all the ones I've seen anyway).

A 29-inch secondary seems huge, but only blocks about 17% of the primary. It looks like there's a path through the middle of the primary, so you'd put the eyepiece/sensor back there; quite convenient, as long as you aren't looking very close to the zenith.

I have no idea how smooth you can make those huge rocker bearings; seems unlikely that this thing would be very good for astrophotography. But man, that's a big bucket.

A 29-inch secondary seems huge, but only blocks about 17% of the primary. It looks like there's a path through the middle of the primary, so you'd put the eyepiece/sensor back there; quite convenient, as long as you aren't looking very close to the zenith.

I have no idea how smooth you can make those huge rocker bearings; seems unlikely that this thing would be very good for astrophotography. But man, that's a big bucket.

There's a photo gallery thing on the article's page that shows the layout better. The eye piece is mounted at an between the primary and secondary mirrors on the side of the truss. The secondary mirror would have to be angled as it would on other dob telescopes.

SpaceBison:Here's one of the primary mirror.[angelgilding.com image 500x484]Glockenspiel Hero: Ok, serious tech question. He's assuming this came off a spy satellite- it's a bit unclear what kind since Wikipedia implies the KH-11s are f1.2 and thus aren't this mirror. Most serious telescopes are not standard Newtonians- the Hubble a Ritchey Chretien, Wiki says the KH-11s are three mirror anastigmats. In either case, the secondary is not a flat mirror- it's curved in some odd way. (RCs are hyperbolic, for example)

Where the fark did he get a curved, 29" secondary? No way did he grind it himself- did it come with the primary?

The secondary mirror on a Dobsonian telescope are flat (at least in all the ones I've seen anyway).

Be careful not to confuse the mount with the optics- Dobs can have any mirror arrangement you want. They're generally parabolic because it's cheap to grind a parabolic mirror and Dobs are all about cheap+big, but spy sats couldn't care less about cheap. I figure he must have gotten the entire optical train or he really is using a flat secondary with a hyperbolic primary, and I have no idea what that would do to the final image

Even a flat secondary is absurd- where do you get a 29" blank? An ordinary mirror is going to bend too much, and a quick Google doesn't turn up anyone selling optical mirrors anywhere close to that size.